EFFECT OF COUNTERION ON THE TRIBOCHARGING OF MOLECULAR-SALT CHARGE CONTROL AGENTS IN XEROGRAPHIC TONERS

A series of model toners were prepared by a solution coating technique . The toner series consisted of equivalent amounts (4 mu mol/g) of neg ative charge control agents (CCAs), 3,5-di-t-butylsalicylic acid (HtBS A) and its metal salts (MtBSA, M = Li, Na, K, Rb, Cs), on the surface of 9 mu m unpigmented styrene-butadiene toner. The morphological prope rties of these CCAs in toner were studied by scanning electron microsc opy, time-of-flight secondary ion mass spectrometry, and fluorescence spectroscopy. Results revealed that CCAs exist in a variety of physica l states on the toner surface: from monomer for HtBSA to dimer or smal l aggregates for LitBSA to higher aggregates or small microcrystals fo r NatBSA, KtBSA, RtBSA, and CstBSA. Charging experiments showed that a ll the toners studied in this work charge negatively against polymer-c oated metal beads and that ion-transfer is the major charging mechanis m. A counterion effect on toner charging was observed. Specifically, t he toner charge becomes less negative as the CCA changes from LitBSA - -> NatBSA --> KtBSA --> RbtBSA --> CstBSA. The counterion effect was a ttributable to either a surface area effect or a thermodynamic effect on the ionization process. The HtBSA toner charged not only less negat ive but also at a slower rate. The anomalously low tribocharge and slo w rate were emphasized in terms of a change in charging mechanism.